1. Field of the Invention
This invention relates to a method for manufacturing a toner, a toner, a fixing device, and an image forming apparatus.
2. Description of the Prior Art
There are known various electrophotographic methods. In general, such electrophotographic methods include a step for forming an electrostatic latent image on a photoreceptor by any means utilizing a photoconductive material (that is, an exposure step), a step for developing the latent image by the use of a toner to form a toner image, a step for transferring the toner image onto a transfer material (recording medium) such as paper, and a step for fixing the toner image by, for example, heating using a fixing roller.
The toner for use in such electrophotographic methods is generally composed of a material containing a resin as a main component (hereinafter, also simply referred to as a “resin”) and a coloring agent.
As for the resin constituting the toner, polyester resin is widely used, because polyester resin has a feature in that it facilitates the control of various properties of a resultant toner (that is, a toner finally obtained), such as elastic modulus, chargeability, and the like.
Further, such polyester resin is composed of a diol component. As for the diol component, aromatic diol such as bisphenol A has been commonly used (see Japanese Patent Laid-open No. Sho 57-109825 (page 1, lines 1 to 27), for example).
However, since polyester composed of such a diol component has a relatively large coefficient of friction and poor mechanical strength (that is, poor resistance to mechanical stress), obtained toner particles are liable to be fractured in a developing device, thus resulting in a case that problems such as poor electrification, contamination of the device, lowering in a fixing property, and the like occur.
Also, there is known a toner which is manufactured using polyester composed of aliphatic diol instead of aromatic diol such as bisphenol A (see Japanese Patent Laid-open No. 2001-324832 (page 2, lines 1 to 13), for example). In such a toner, a polyester block copolymer, which contains in its molecule a block obtained by condensation of aliphatic diol with carboxylic acids and a polyester block obtained by condensation of alicyclic diol with carboxylic acids, is used as polyester resin. However, a problem exists with such a toner in that a temperature range in which a sufficient fixing property (fixing strength) is ensured is narrow.
Further, as for a method for manufacturing a toner, a grinding method, a polymerization method, or the like is commonly employed.
In a grinding method, a material containing a resin as a main component (hereinafter, also simply referred to as a “resin”) and a coloring agent is kneaded at a temperature higher than the softening point of the resin to obtain a kneaded material, and the kneaded material is then cooled and ground. Such a grinding method has an advantage in that various materials can be selectively used and a toner can be manufactured with relative ease. However, a toner obtained by the grinding method has a disadvantage in that there are large variations in shapes of individual particles of the toner and the particle size distribution of the toner also tends to be wide. As a result, variations in charging properties, fixing property and the like among the toner particles also become large, thus resulting in reduced reliability of the toner as a whole.
In a polymerization method, a polymerization reaction is carried out in a liquid phase using a monomer which is a constituent component of a target resin to obtain a raw resin, by which toner particles are manufactured. Such a polymerization method has an advantage in that toner particles having a shape with relatively high sphericity (that is a shape close to a perfect geometrical sphere) can be obtained. However, in a case where the polymerization method is employed, there is a case where a variation in particle size among individual toner particles can not be made sufficiently small. Further, in the polymerization method, the range of choices of resin materials is narrow so that there is a case where it is difficult to obtain a toner having target properties.